HUP doesn't send to processes when logout

[Rick Stevens]

ƽÌ캫 wrote:
> 2008/12/30, Rick Stevens <ricks at nerd.com>:
>> Jerry Feldman wrote:
>>> On 12/29/2008 04:56 PM, ƽÌ캫 wrote:
>>>> 2008/12/30, Jerry Feldman <gaf at blu.org>:
>>>>
>>>>> On 12/29/2008 10:05 AM, ƽÌ캫 wrote:
>>>>>
>>>>>> hi,
>>>>>>
>>>>>> It seems that when I logout from the console, the background process
>>>>>> doesn't get HUP signal:
>>>>>> { trap "echo Ignore HUP >>/tmp/trap.out" 1; while sleep 3;do echo
>>>>>> hello >>/tmp/hello.txt;done; }&
>>>>>> And it seems it will become a daemon and run forever until rebooting.
>>>>>> Is this correct? Why it didn't get HUP signal?
>>>>>>
>>>>>> Thanks!
>>>>>>
>>>>>>
>>>>>>
>>>>> Are you running this from a terminal window?
>>>>>
>>>> I am running this in tty2, a console. I just type those into the
>>>> console and run it, then logout.
>>>>
>>>>
>>>>> Are you possibly setting nohup in your environment.
>>>>>
>>>> It seems it is. But how?
>>>>
>>>>
>>>>> Are you typing the above commands directly? What happens if you place
>>>>> these into a script and run the script in the background?
>>>>>
>>>>> There are a number of things that can cause a shell script to ignore the
>>>>> HUP signal. I tested this as a script on an Ubuntu laptop, and it
>>>>> behaved the same as yours:
>>>>>
>>>>> The process remained. So the issue is not that exiting the parent
>>>>> process (GNOME Term) or logging out of GNOME fails to issue a HUP, it is
>>>>> that the process itself ignores the HUP signal since I sent a "kill -HUP
>>>>> <pid>" to the process.
>>>>>
>>>>> If you simply send the HUP signal, you will see that "Ignore HUP" will
>>>>> appear in /tmp/trap.out".
>>>>>
>>>>>
>>>> I have the same results with you.
>>>>
>>>>
>>>>> The signal(1) command is probably the culprit, though the man pages are
>>>>> vague.
>>>>>
>>>>>
>>>> I suspect of that maybe the logout doesn't send out HUP to these
>>>> background processes?
>>>>
>>> After looking at this again now that I understand the specific issue. I
>>> would agree.
>> By default, the "huponexit" option is NOT set on bash shells, so a
>> terminating interactive shell does NOT send HUPs to background
>> processes.
>>
> 
> Thank you very much for pointing this out.
> 
>> Try it again, but run "shopt -s huponexit" before executing the
>> background process.  When you log out, HUPs should be sent to child
>> processes.
> 
> Yes, I have seen the HUP signal being sent to the background process
> if set the "huponexit".
> 
> But even though i ignore HUP in the background process, it quits every
> time when logout, after
> echo a line of "Ignore HUP" to /tmp/trap.out. What's wrong?

Because while a logout doesn't send a HUP unless huponexit is set, it
DOES send a TERM signal which should terminate child processes.  You
need to trap that signal as well or use a "disown" on the PID of the
child process to disassociate it from the login shell.
----------------------------------------------------------------------
- Rick Stevens, Systems Engineer                      ricks at nerd.com -
- AIM/Skype: therps2        ICQ: 22643734            Yahoo: origrps2 -
-                                                                    -
-            "You think that's tough?  Try herding cats!"            -
----------------------------------------------------------------------